Most vehicle interior materials are subject to grain finish with such as a leather pattern, a geometric pattern, or the like, on the surface thereof. The grain finish is performed in order not only to improve design and texture of the surface of an interior material but also to make shrinkage or weld marks on the surface of a product after molding inconspicuous, or the like.
A grain structure provided on the surface of a product includes convexities and concavities provided in predetermined patterns. By appropriately adjusting the quality of materials or the surface roughness of convexities and concavities of a portion constituting the grain structure, it is possible to improve the texture quality of a product and to enhance the durability thereof against abrasion. Generally, it is possible to provide a product with a high texture quality by lowering the surface glossiness of the product to a certain extent. If the surface glossiness is overly lowered, however, there is a tendency that abrasion marks are left on the surface when the surface is abraded, surface whitening occurs, or the like. For this reason, the surface glossiness is adjusted taking balancing these factors into consideration (refer to Patent Document 1).